Data centers and server racks are extremely noisy places. The noise resulting from vibration can be significant. Multiple sources of vibration contribute to the vibration level of server racks in data centers including but not limited to Computer Room Air Conditioners (CRACS) for building and racks, chillers, building, rack, and server transformers, building/rack Un-interruptible Power Supplies (UPS) and rack/server/Hard Disc Drives (HDD) and cooling fans. These are all very noisy and collectively create a very complex and high level of vibration at wide ranges of frequency. Vibration levels at data centers, server racks and servers vary and typically can be 1 g or more.
Existing server racks are fabricated without vibration dissipating measures. Generally made from steel sheet metal, existing rack structures actually magnify vibration rather mitigating it.
Hard Disc Drives are very sensitive to vibration. When looking for a file to read, the head is moving inward or outward as the disc is spinning, in order to locate the beginning of the file. Vibration makes this task more difficult as the head searches for the file location on the disc. HDD manufacturers have implemented vibration sensors in the HDDs to sense vibration and pause I/O operation in presence of high vibration. Input/Output (I/O) becomes much faster and more efficient as vibration is suppressed. Generally, write operations take longer than read operations and are more sensitive to vibration. Many server/computer operations are I/O—intensive workloads, e.g. On-line transaction processing (OLTP) applications, video streaming, web serving, finance applications, etc.
Vibration at wide ranges of frequencies interferes with HDD operation and in some cases causes the corresponding server or computer to shut down. As a result, there is a need for anti-vibration measures at various frequencies to dissipate vibration in servers allowing HDDs to perform much more efficiently.
The relationship between an arbitrary vibration force F and the resulting motion X of a multiple degree of freedom structure can be presented as: MX″+CX′+KX=F
Where X is displacement (motion), X′ velocity, X″ is acceleration, M represents mass, C damping and K stiffness of the structure. Stiffness and damping properties of materials and structures vary with operational frequencies.
Embodiments of the novel anti vibration rack optimize structural stiffness and damping to mitigate vibration at all operating frequencies in servers and data centers.
The selection of materials may also influence the performance of a system. Materials that aid in minimizing vibration exist. An example of such is carbon fiber composites.
Carbon fiber generally refers to carbon filament thread, or to felt or woven cloth made from those carbon filaments. The term carbon fiber is also used to mean any composite material made with carbon filament, such a material is sometimes referred to as graphite-reinforced plastic.
Each carbon filament is made out of long, thin filaments of carbon sometimes transferred to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer used in the creation of many synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing continuous filaments. When heated in the correct conditions, these chains bond side-to-side (ladder polymers), forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped or round filament. The result is usually 93-95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000° C. (carbonization) exhibits the highest tensile strength (820,000 psi or 5,650 MPa or 5,650 N/mm2), while carbon fiber heated from 2500 to 3000° C. (graphitizing) exhibits a higher modulus of elasticity (77,000,000 psi or 531 GPa or 531 kN/mm2).
There are several categories of carbon fibers: standard modulus (250 GPa), intermediate modulus (300 GPa), and high modulus (>300 GPa). The tensile strength of different yarn types varies between 2000 and 7000 MPa. The density of carbon fiber is 1750 kg/m3.
Precursors for carbon fibers are PAN, rayon and pitch. In the past rayon was more used as a precursor and still is for certain specialized applications such as rockets and specific aerospace applications. Carbon fiber filament yarns are used in several processing techniques: the direct uses are for prepregging, filament winding, pultrusion, weaving, braiding and the like.
The filaments are stranded into a yarn. Carbon fiber yarn is rated by the linear density (weight per unit length=1 g/1000 m=tex) or by number of filaments per yarn count, in thousands. For example 200 tex for 3,000 filaments of carbon fiber is 3 times as strong as 1,000 carbon fibers, but is also 3 times as heavy. This thread can then be used to weave a carbon fiber filament fabric or cloth. The appearance of this fabric generally depends on the linear density of the yarn and the weave chosen. Carbon fiber is naturally a glossy black but colored carbon fiber is also available.
Carbon fiber may be used to reinforce composite materials, particularly the class of materials known as carbon fiber reinforced plastics. This class of materials is often used in demanding mechanical applications. Carbon fiber's unique properties such as high stiffness, high strength, high damping, low density, and corrosion resistance are ideal for demanding applications. Carbon fiber/epoxy composites have mechanical properties such as the stiffness and strength of steel, and damping of 10 times more than aluminum at 30% lower density.
While non-polymer materials can also be used as the matrix for carbon fibers, due to the formation of metal carbides (i.e., water-soluble AlC), bad wetting by some metals, and corrosion considerations, carbon is used less frequently in metal matrix composite applications.
Vibration may interfere with the operation of HDDs, cooling fans and other server components resulting in reduction of performance and increase in energy consumption. Therefore there is a need for a means to minimize or eliminate vibration. In order to address the vibration, embodiments of the present invention provide for a novel anti-vibration rack (AVR) that dissipates vibration at wide frequency ranges. For example, the novel AVR may dissipate vibration from 10 Hz to several thousand and perhaps in several hundred thousand Hz. The frequency range of interest in HDD operation is preferably from 50 Hz to 2,000 Hz. Testing of various embodiments of the novel server AVR verify the effect of its anti-vibration technologies on servers' performance and energy consumption. Embodiments of the novel AVR dissipate vibration passively, effectively eliminating vibration in all interested frequency ranges.